The present invention relates to an active matrix type liquid crystal display apparatus, particularly, to an active matrix type liquid crystal display apparatus of the in-plane switching type, wherein a liquid crystal is driven by generating and applying an electric field nearly in parallel to the surface of the substrate.
Display of information by a liquid crystal display apparatus is performed by applying an electric field to liquid crystal molecules in a liquid crystal layer interposed between substrates to change the orientation of the liquid crystal molecules and to utilize the change in the optical properties of the liquid crystal caused by the change of the orientation of the liquid crystal to produce a display.
An active matrix type liquid crystal display apparatus of a twisted nematic display (TN) type is typical of a conventional active matrix type liquid crystal display apparatus. In the active matrix type liquid crystal display apparatus of a twisted nematic display type, display of information by the liquid display apparatus is performed by applying an electric field nearly perpendicular to the surface of the substrate to the liquid crystal and utilizing the optical rotating power of the liquid crystal to control optical properties of a display. On the other hand, an active matrix type liquid crystal display apparatus of an in-plane switching type has been proposed, for example, in Japanese Patent Laid-Open No. 63-21907.
In the active matrix type liquid crystal display apparatus of an in-plane switching type, display of information by the liquid crystal display apparatus is performed by applying an electric field nearly in parallel to the surface of a substrate using interdigitated electrodes and utilizing birefringence of the liquid crystal to control optical properties of the display. The in-plane switching mode has the advantages of providing a wider viewing angle and lower storage capacitance compared to the conventional twisted nematic type and, accordingly, is a promising technology for the active matrix type liquid crystal display apparatus.
With the recent trend of high speed response of the active matrix type liquid crystal display apparatus, there occurs a display problem in the form of a so-called after image in the liquid crystal display elements, that is, an image retention phenomenon. The term image retention phenomenon, that is, the after image problem, refers to a state wherein there occurs a zone having a very slow response compared to a normal liquid crystal response speed of approximately 50 milliseconds. Occurrence of the after image phenomenon in the conventional twisted nematic type liquid crystal display apparatus is caused by accumulating a direct current charge in a boundary surface of a liquid crystal alignment layer of each pixel to change the effective voltage. In other words, the after image phenomenon is caused by the fact that an electric potential at the time of application of the voltage is not eliminated within the response time and is held in the alignment layer on the pixel electrode or the boundary surface of the liquid crystal alignment layer to change the effective voltage applied to the liquid crystal layer. The relationship between the after image phenomenon and the residual direct current voltage component has been studied, and, at the present time, it is being suggested that the after image phenomenon can be improved by decreasing the residual direct current voltage. Therefore, as the alignment layer of the conventional twisted nematic mode, an alignment layer having a property of hardly accumulating a direct current charge, that is, having less residual direct current voltage component, is required.